The present invention relates to optical encoders. More specifically, the present invention relates to an improved reference point optical encoder.
Diffractive optical encoders are well known in the field of position displacement sensing systems. Such devices are commercially available from the assignee of the present invention as well as from several other vendors. U.S. Pat. Nos. 5,559,600 and 5,646,730 describe examples of known optical encoders.
A recent trend has been to develop diffraction based encoders of reduced size. U.S. Pat. Nos. 5,995,229; 5,671,052; 5,909,283; and 5,991,249 disclose examples of such reduced size encoders. Generally, such reduced size encoders are characterized by their use of a solid-state source of quasi-monochromatic (or nearly monochromatic) illumination, a binary grating, one or more detecting elements, and a reduced number of additional optical components.
One problem with the known reduced size encoders is that the size reduction has generally had a negative impact on their accuracy. Accordingly, there is a need for reduced size diffractive optical encoders characterized by improved accuracy.